The present invention relates to a navigation and guidance system providing heading correction data to guide to, or maintain a vehicle on, a predetermined course. As used herein, the term vehicle encompasses any suitable manned or unmanned mobile craft, vehicle, missile or means of conveyance, adapted for movement on or through air, water, space or land.
Many tasks necessitate the navigation of a predetermined route across/through a particular section of land, water surface, seabed, air space or celestial body, including agricultural spraying, geographic surveying, SAR operations, boating man overboard recovery, fire fighting, penetrating hostile airspace and so forth. In many applications, the exact adherence to the predetermined course is degraded by external factors such as wind and tides, internal factors such as system inaccuracies and performance limitations together (when present) with human operator error.
There is often a need to determine the corrective course heading necessary to restore a vehicle to a predetermined course in the most expeditious manner. This may be most simply effected by guiding the vehicle straight to the closest point of the predetermined course. However, due to the intrinsic response latency of both the system and pilot together with the performance characteristics of the vehicle, a corrective heading guiding directly to the closest point of the predetermined course invariably results in the vehicle repetitively overshooting the predetermined course generating lateral oscillations about the predetermined course. This may be avoided if the vehicle came to rest at the point intersection with the predetermined course and was then turned to resume motion along the predetermined course. However, this solution would be unfeasible and undesirable in many dynamic applications employing relatively high-speed vehicles such as in aerial crop-spraying. Furthermore, in many timecritical applications, it is often more effective to bring the vehicle back on course whilst maintaining progress in the direction of the predetermined course without an appreciable reduction in velocity. This requires the vehicle to take a corrective course continuously converging with the predetermined course until coincident with same.
The development of satellite navigation such as Global Positioning System (GPS) provides a means of readily establishing a vehicle""s position, its actual course and calculating its displacement from a predetermined course or waypoint. However, in order to provide a corrective heading for an off-course vehicle, a specific destination point on the predetermined course is required. Other than the direct course to the closest point of intersection (with the attendant disadvantages discussed above) specifying any other arbitrary point on the predetermined course would clearly result in an equally arbitrary guidance solution.
Existing prior art solutions utilize the judgment of the vehicle""s pilot to interpret a display representing the linear displacement of the vehicle from the closest point of the predetermined course. A lightbar consisting of a row of light emitting diodes (LED) denotes the vehicle""s deviation to the left or right of the swath by respectively illuminating a proportional number of LEDs to the left or right of a central xe2x80x98on coursexe2x80x99 LED.
The finite resolution of the lightbar (e.g. one LED=30 cm), together with the absence of any corrective heading data results in course oscillations about the swath centre line as the pilot attempts to remain within the tolerance/resolution of the display means. Whilst replacing the corrective displacement indicator with a corrective heading would ameliorate the disadvantages described herein, there remains the hitherto unresolved problem of which point on the predetermined course to guide to. This problem is further exacerbated if the predetermined course is non-linear.
The above described need to restore and maintain a particular vehicle/entity along a defined path is not solely restricted to physical vehicles in the conventional sense of the term. This requirement is equally applicable to non-physical vehicles or entities, such as computer-generated xe2x80x98virtualxe2x80x99 objects/entities in applications such as, navigation and flight/steering simulation software and the motion control of vehicles/objects/figures/guided projectiles and entities types in computer games.
There are numerous other non-vehicular applications or processes which also require the maintenance of dynamic control of two or more variables in accordance with an optimum predetermined mathematical solution, wherein the actual instantaneous numerical value or quantity of the said variables would analogous to the xe2x80x98vehiclexe2x80x99 location in the above described applications. The desired predetermined course of the xe2x80x98vehiclexe2x80x99 could be represented by a plot of the optimum solution with respect to time (or some other irreversible quantity). As an example, the desired solution/predetermined course could be the instantaneous ratio (which may vary over time) of two or more chemical constituents being continuously combined as part of an industrial process. In this instance, any variation of the ratio of the constituents from the desired solution would be equivalent to a displacement of a physical vehicle from a predetermined course. The ideal corrective action to the input (or output) rate of one or more of the constituents to obtain the desired ratio is governed by directly equivalent criteria to that described above in the vehicular application, i.e. a critically damped, non-oscillating return to the correct ratio.
Consequently, despite the differing nature of the above described applications and though in some instances grammatically unorthodox, consistent terminology will be used throughout the specification for the sake of succinctness and clarity, wherein the following definitions of key terms shall apply in both the description and claims.
the term xe2x80x98vehiclexe2x80x99 is any object or quantity whose location may vary with respect to some irreversible variable such as time and encompasses any suitable manned or unmanned mobile craft, vehicle, missile or means of conveyance (including simulated, virtual or software generated vehicles or entities), adapted for movement on or through air, water, space, land or any other real, simulated, virtual or mathematically generated environment and also includes dynamic numerical values attributed to particular quantities, ratios and/or other parameters.
the term xe2x80x98locationxe2x80x99 is defined as a point of interest, a real or imaginary postion in a two, three or more dimensional space, or a coordinate in any convenient co-ordinated system.
the term xe2x80x98corrective headingxe2x80x99 includes a conventional heading change, such as a change of heading, pitch, roll or yaw or a set of partial derivatives, such as a change in pressure, temerature or speed with respect to time.
the term xe2x80x98predeterminedxe2x80x99 includes any physical, virtual, geographical path or mathematical solution representing the desired location for the vehicle location.
It is object of the present invention to provide a means for guiding to linear and non-linear guidance curves/courses or solutions which overcomes the aforesaid disadvantages.
It is a further object of the present invention to provide corrective data to mitigate any deviation of a vehicle from a predetermined course by progressively re-aligning the vehicle""s heading to coincide with the predetermined course whilst minimizing any discontinuities or excessive course oscillations.
The present invention provides a guidance system for a vehicle and a method for executing same, comprising;
navigation system capable of providing vehicle location information including the position of said vehicle,
a data storage means capable of storing at least one pre-determined course having a preferred direction of travel,
a processing means capable of receiving the said vehicle location information, calculating the magnitude of any displacement of said vehicle from said predetermined course along a direct path to the closest point of said predetermined course and thereupon generating an intermediate waypoint at a predetermined response distance from said vehicle at a point along a composite line formed by the shortest route from the vehicle to a point of intersection with the predetermined course and extending thereupon along the said predetermined route in said preferred direction for a distance along said composite line equal to said predetermined response distance, calculating the heading from the vehicle to the intermediate waypoint and outputting same as a corrective course heading.
The vehicle heading is then altered in accordance with the corrective course heading, either automatically or manually by a user and the new vehicle postion and heading is detected after a predetermined time interval, whereupon an updated corrective course heading is calculated.
The magnitude of said predetermined distance may be a function of one or more of said vehicle location parameters or be a simple fixed value.
One or more elements of the above vehicle guidance system may be located either onboard or external to the vehicle.
As used herein, the various headings referred to may be defined in accordance with any convenient frame of reference, e.g. magnetic/compass bearings, relative to a local grid or waypoints, Cartesian co-ordinates and so forth.
These and other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description. The various features of novelty which characterize the present invention are detailed in the claims annexed hereto and form part of this disclosure. To provide a clear understanding of invention and its advantages attained through its use, reference is made the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.